Animal feeds are supplemented with individual amino acids according to the needs of the animals. For supplementing animal feeds with L-lysine for example, L-lysine monohydrochloride with an L-lysine content of 78% has hitherto been used in by far the majority of cases. To produce the monohydrochloride, the L-lysine, which is prepared by fermentation, first has to be separated from all other constituents of the crude fermentation broth in complicated process steps, subsequently converted into the monohydrochloride and crystallized. A large number of secondary products and the reagents required for working up accumulate as waste. Since high purity is not always required of the animal feed supplement and since, in addition, the secondary fermentation products often contain substances of nutritive value, there has been no shortage of attempts in the past to avoid the expensive production of feed-quality amino acids, more particularly pure L-lysine monohydrochloride, and to convert the crude fermentation broth less expensively into a solid animal feed. Unfortunately, none of these attempts has produced an economically useful result.
A serious disadvantage has been the complex composition of such media because, in general, they are difficult to dry, are hygroscopic, do not flow freely and are susceptible to agglomeration, and they are unsuitable for technically demanding processing in mixed feed factories. Above all, fermentation products of lysine are particularly disadvantageous in this regard. The simple removal of water from the crude fermentation broth by spray drying leads to a dusty, highly hygroscopic concentrate which forms lumps after only brief storage and which cannot be used as an animal feed in this form.
In order to obtain a free-flowing, storable product, a large quantity of various additives has to be incorporated in the concentrate. However, this further reduces the often already relatively low content of the amino acid. One such product is described, for example, in Published German Patent Application DE-OS 23 57 119, according to which a concentrate is prepared from the fermentation broth, optionally after removal of the biomass, and auxiliary substances are subsequently added to the concentrate thus prepared. Alternatively, the lysine may also be released from the concentrate by precipitation with methanol. Additive-containing feed supplements produced by fermentation are also described in DD 139 205, in Upr. Mirkrobn. Sint. 111-118 (1973), in CA 105 (19): 170542g, in DE 30 32 618 (U.S. Pat. No. 4,327,118) and in Patent CS 250 851.
European Patent EP 122 163 (U.S. Pat. No. 5,133,976) describes a process by which it is possible under special fermentation conditions to obtain a crude fermentation broth which can be dried to form a solid and stable product. However, in this case, too, the L-lysine content is only 35 to 48% by weight. It is also known from these documents that the removal of water by azeotropic distillation with paraffin oil leads to acceptable products. However, this process is also complicated and expensive. Tetrachloromethane, which is toxicologically unsafe, has also been similarly used (CS 164 706).
The use of a spray dryer with an integrated fluidized bed gives a fine-particle and porous, but free-flowing granular product of very low apparent density and high hygroscopicity. The handling of this product is accompanied by serious dust emission.
Pelletizing in a fluidized bed has also proved to be unsuitable because it also involves the use of additives which, according to Patent DD 268 865, are continuously added. The use of the additives is essential to bind the water from the fermentation broth so as to prevent the pellets from agglomerating which would have a particularly adverse effect on pelletizing.